Membrane technologies have shown tremendous potential for a variety of separations, and new applications are constantly appearing. These new applications require exploration of materials, operational conditions, and membrane synthesis procedures, and demand accurate and timely evaluation of membrane properties and performance. Many different membrane materials may need to be screened in order to determine the most appropriate membrane for a separation application, and the large variety of potential membranes and the numerous parameters which may be varied generates a laborious and time intensive testing process using typically available methods.
Two general methods for membrane material evaluation are the variable-pressure method and the variable-volume method. In the variable-pressure method, a gas permeates through a film into a closed constant-volume chamber that is pre-evacuated, and the pressure rise in the chamber is recorded as a function of time. In the variable-volume method, the chamber into which a gas permeates is allowed to expand against a low constant pressure, and the volume change of the chamber is recorded as a function of time. The methods are widely used for the determination of steady-state permeation rates for pure gases.
For membrane evaluation when a prospective feed gas is a gas mixture, continuous flow is generally utilized in both the supply chamber and receiving chamber of a permeate cell, in order to avoid the build-up of concentration gradients in the cell. In general, the permeation rate will be different for each gas species in a gas mixture and continuous flow on both the retentate and permeate sides of a membrane during testing acts to mitigate the concentration gradients.
There is a huge variety of potential membrane materials for gas separations involving mixed gases. Additionally, the testing is often required to be conducted under a varying range of conditions, since membrane performance is typically dependent on a variety of factors such as feed pressures, temperatures, pH, feed concentrations, and so on, generating a large number of candidate membranes. It would be advantageous to provide a system whereby the testing of multiple membranes under substantially identical conditions could occur, in order to more rapidly evaluate a large number of candidate membranes for a given gas separation application. It would be additionally advantageous if the system operated in a continuous flow manner on both the retentate and permeate sides of the membrane, in order to allow effective evaluation against various gas mixtures. It, would be further advantageous if the system were designed such that while sampling the permeate and retentate gases of a given membrane, the non-tested membranes remained subject to the substantially the same conditions on both the permeate and retentate sides throughout the sampling rotation, so that performance over extended periods of time could be adequately evaluated.
Provided here is a membrane testing system providing the capability to test a plurality of planar membranes subjected to a feed gas on one side and a sweep gas on a second side. The membrane testing system continuously provides a pressurized and continuous flow of the feed gas and the sweep gas to each membrane testing cell while retentate and permeate streams are continuously withdrawn. The retentate and permeate streams of the plurality of membrane testing cells are ported to either a mass flow controller or a backpressure regulator by multiport valves, acting to maintain substantially equivalent pressures and flow rates on each planar membrane throughout a sampling cycle. The system allows the testing of multiple membranes under substantially identical conditions for rapid evaluation of candidate membranes for given gas separation applications and various gas mixtures, and maintains substantially constant conditions on both the permeate and retentate sides of non-sampled membranes with continuous flow throughout a sampling rotation, allowing consistent evaluation over extended periods of time.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.